a. Field of the Invention
The present invention relates to an electric shutter for cameras and, more particularly, to a programmed type electric shutter arranged so that the diaphragm aperture and shutter speed will be automatically set according to brightness of the object to be photographed.
B. Description of the Prior Art
Some known program-type electric shutters are arranged to operate a diaphragm means positioned in front of a light-receiving element, according to exposure characteristics of the shutter, so as to establish the diaphragm aperture. Others are arranged to continuously vary the voltage developed by a comparison circuit or to vary a comparison resistance stepwise, in order to determine the diaphragm aperture, according to exposure characteristics of the shutter. The former has a disadvantage that exposure becomes inaccurate, when a photoelectric element such as CdS is used, because of delay of response. The latter has various problems in its performance and durability because many contacts are required for changing a variable resistor on switching among resistors. Moreover, known shutters of this type generally have a disadvantage in that the shutter mechanism becomes complicated.